The term POP (Persistent Organic Pollutants) is used to designate a set of substances that share four characteristics in an especially hazardous combination: 
1. they are highly toxic to man and the environment;
2. they accumulate in the adipose tissue of living beings (we call it bio-accumulation) and can be transmitted to the progeny through breast milk or through eggs, depending on the species;
3. they persist over years or even decades before degrading into less hazardous forms;
4. they evaporate and travel long distances in air and in water to be deposited far from their place of origin.
In the upcoming section you will find some actual examples clearly illustrating the properties of these toxic substances.
The main sources of these substances are:
- intentional production of chemical products such as pesticides
- non-intentional production that results from human activity especially activity related to industry, transportation and the residential sector (for example the highly toxic dioxins and furans).
Considering the characteristics of POPs, the management of risks associated with these substances requires a global response at an international, European and national level.